Tried Vonage out about 6 months ago, not working so great these days. I am doing webex demo's and the since there is no bandwidth shaping, my voice quality is dying out when I send alot of data out (screen updates during demos). I ordered AT&T Callvantage since Nick recommended it and the box can sit outside the firewall without hanging (like the Vonage MTA) and does traffic shaping to guarantee bandwidth for the voice portion. I tried a tc script from http://www.vonage-forum.com/ftopic1104.html to see if that would resolve the problem but it continues to be a problem. Unfortunately AT&T only supports single line so the business line will have to stay on Vonage until they iron out that issue. Vonage also forgot to cancel my line with Qwest so they have been charging me $30/mo since I switched for basically nothing but a forwarding line. I may be getting a refund for these costs from Vonage according to an email I got today:
Thank you for contacting Vonage.
In responses to your question, currently we are working on your request. Once the transfer has been completed you will be issued credit for the time lost after the 20 business days.
Please let us know if we may be of any further assistance.
Keeping my fingers crossed.